GrandmaJones hit on it...
A lot of JWs, in trying to maintain a simple lifestyle while spending as much time in Kingdom work slavery to the WTS, would work in part-time jobs, sometimes in what some people might call "unskilled" labor such as janitorial. Some brothers instead of working for someone else, would start their own services so they could set their own work schedule thus leaving service schedules easy to make.
It is a flip way of referring to them, but it's not always fair. Some "brothers" have made very good livings in the cleaning business. Some brothers have invented gadgets for the cleaning industry that has made them rich.
In the end though, many elders are still uneducated, manual laborers who are sitting in judicial meetings counseling people who have been abused by predators in the congregation. These men, no matter how succesful they are in cleaning windows or organizing construction crews have no credentials for doing the work of the police, courts or therapists.